#include <algorithm>

template<typename T>
struct foo
{
  T t;
  foo():t(0){}
  void swop(foo& x)
  {
    using std::swap;
    swap(t,x.t);
  }
};

template<typename T>
void swap(foo<T>& x,foo<T>& y)
{
  x.swop(y);
}

int main()
{
  foo<int> x,y;
  x.swop(y);
}